Which is actually a more reasonable position. For example, if there aren't any other passengers around, what is the harm? (George Berkeley would be proud...)
Your version would require the traincrew to take action.
Only when there is no other passenger in the coach is it OK. Very, very rare for that to be the case.
Think of it from the point of view of, say, a slightly built woman in a coach with a hefty, rough looking man playing music out loud*. She is likely to fear saying something (to evidence the annoyance) because he may be a threat to her. Should she have to put up with it?
Better that it is absolute. I'm not saying trains need to be like libraries, of course it is OK to talk etc, but electronic devices should always be used with headphones. Splitters are available if multiple people want to watch the same thing.
* I'm more like the latter, and once did ask a family to leave Coach A on a Virgin train because they were playing films out loud on tablets. They did leave, and I got a round of applause (ssh, that's not quiet

), but I doubt they would have been willing to challenge me were I the guilty party, for their own safety.
This leads me to the (no doubt controversial) view that I would be willing to pay a premium to travel in a quiet carriage.
I usually go for A because it has the best seat in the house - seat 45 - subdued lighting, aligned window and extra legroom as well as floor space for large luggage behind the row opposite, but it is nice that it's quiet, too. I would pay to select that seat, though I'm glad Trainsplit lets me for nowt.